The present invention relates generally to control systems, and more particularly to an improved system for automatically controlling the operation of home appliances and other electrically operated devices, such as lamps and television receivers.
As the number and usage of electrically operated devices, such as kitchen appliances, lamps and home entertainment products, has increased so has the desire of the homeowner and apartment resident to be able to establish and control the operation of these devices remotely and in an automated manner. For purposes of increased security and convenience, a homeowner may wish to cause a number of lamps and appliances throughout the house to be automatically turned on and off at preset times which may vary for different days of the week. Thus, for example, a homeowner may wish the coffee maker to be automatically turned on before he arises and the hall lights to be turned on before he arrives from work and turned off after he retires.
One prior approach to automated appliance control is disclosed in U.S. Pat. No. 4,200,862, assigned to the assignee of the present application, the disclosure of which is herein incorporated by reference. The control system disclosed in that patent includes a transmitter unit in which the module addresses and operating information concerning the appliances to be controlled automatically can be entered. The transmitter unit is connected to an a.c. power line, which transmits address and control signals in the form of binary coded bursts or pulses over the a.c. power line to a plurality of control modules also connected to the a.c. power line that control the operation of the electrical appliances, lamps, television sets, and the like that are respectively connected to the modules. The binary coded signals that are transmitted along the ac power line to the modules identify each of the modules by their address and control the operation of the electrical devices, that is, for example, turn them on or off, or dim them in the case of lights, at prescribed times.
In the apparatus control system disclosed in the '862 patent, the bursts or pulses that constitute the binary address and control signals are synchronized to the zero crossing points of the a.c. power line; that is, they are produced near or at the zero crossing points of the a.c. power. These pulses are received and detected at the modules and are then decoded to derive the address and control signals.
Although this system has proven to be highly successful over the years, certain drawbacks in it have became apparent. By limiting the detection of the absence or presence of a logic "one" signal only to the a.c. power line signal zero crossing points, the number of operating module binary address and control codes that can be generated during a given period of time is limited. It has also been found that the presence of noise on the ac power line could be mistaken by the module control units as a binary bit or logic "one" signal that could result in an erroneous operation of the module.